Hyperglycaemia induced by chronic i.p. and oral glucose loading leads to hypertension through increased Na+ retention in proximal tubule

Na,K-ATPase Kinetics and Oxidative Stress in Kidneys of Zucker Diabetic Fatty (fa/fa) Rats Depending on the Diabetes Severity-Comparison with Lean (fa/+) and Wistar Rats

For a better insight into relations between type 2 diabetes mellitus (T2DM) and Na,K-ATPase properties in kidneys, we aimed to characterize two subgroups of ZDF obese (fa/fa) rats, with more and less developed T2DM, and compare them with two controls: lean (fa/+) and Wistar. Na,K-ATPase enzyme kinetics were estimated by measuring the ATP hydrolysis in the range of NaCl and ATP levels. As Na,K-ATPase is sensitive to oxidative stress, we evaluated selected oxidative stress parameters in kidney homogenates. Our results suggest that thiol-disulfide redox balance in the renal medulla and Na,K-ATPase properties in the renal cortex differ between both controls, while observed measurements in lean (fa/+) rats showed deviation towards the values observed in ZDF (fa/fa) rats. In comparison with both controls, Na,K-ATPase enzyme activity was higher in the renal cortex of ZDF rats independent of diabetes severity. This might be a consequence of increased glucose load in tubular fluid. The increase in lipid peroxidation observed in the renal cortex of ZDF rats was not associated with Na,K-ATPase activity impairment. Regarding the differences between subgroups of ZDF animals, well-developed T2DM (glycemia higher than 10 mmol/L) was associated with a higher ability of Na,K-ATPase to utilize the ATP energy substrate.

Association between glycated hemoglobin and ambulatory blood pressure or heart rate in hypertensive patients

OBJECTIVES

To determine the association between glycosylated hemoglobin (HbA1c) and ambulatory blood pressure or heart rate in hypertensive patients.

METHODS

A total of 585 patients, who performed ambulatory blood pressure monitoring (ABPM) from September 2018 to April 2019 in Xiangya Hospital, Central South University, were enrolled and assigned into 2 groups (470 in a hypertensive group and 115 in a normal group). HbA1c levels were compared. According to the HbA1c level, the hypertensive group was divided into 2 subgroups: A high HbA1c group (HbA1c≥6.1%, n=142) and a normal HbA1c group (HbA1c<6.1%, n=328). Whole basic data and ABPM parameter were compared among the groups. Pearson/Spearman correlation analysis was applied to study the association between HbA1c and BPV. Multivariate logistic regression was used to explore the influential factors for HbA1c (≥6.1%) and continuous increase of HbA1c in different hypertensive populations, respectively.

RESULTS

The hypertensive group had higher HbA1c level than the normal group [(6.1±1.3)% vs (5.1±1.7)%, P<0.05]. In hypertensive patients, nocturnal systolic blood pressure [(131.1±19.2) mmHg vs (122.5±19.2) mmHg], nocturnal systolic blood pressure load [62.5% (15.5%-100%) vs 28.6% (0-75%)], and daytime heart rate [(74.3±11.6) min-1 vs (71.2±11.4) min-1] of the high HbA1c group were higher than those in the normal HbA1c group (all P<0.05). Pearson/Spearman correlation analysis showed that HbA1c was positively correlated with systolic blood pressure and blood pressure load (both P<0.05). Logistic regression analysis showed that nocturnal systolic pressure load was the risk factor for the increase of HbA1c level (OR=1.025, 95% CI 1.003 to 1.048, P<0.05). Multiple linear regression showed that nocturnal systolic pressure load was still positively correlated with HbA1c in total, tertiary, and hypertensive patients without treatment (β=0.155, β=0.171, β=0.384, respectively, all P<0.05).

CONCLUSIONS

In hypertensive patients, HbA1c is positively correlated with ambulate blood pressure, blood pressure load, and heart rate, and it has no correlation with blood pressure variability, heart rate variability, or morning blood pressure.

Role of carnitine in regulation of blood pressure (MAP/SBP) and gene expression of cardiac hypertrophy markers (α/β-MHC) during insulin-induced hypoglycaemia: Role of oxidative stress

Cardiovascular disease is a leading cause of death in diabetic patients. Hyperglycaemia and iatrogenic hypoglycaemia exacerbate several pathogenic mechanisms underlying hypertension and heart diseases. Carnitine is a potent endogenous antioxidant and cellular fatty acid transporter for antioxidative stress and energy production in the cardiovascular system. The current study aimed to find the role of carnitine in the regulation of hypoglycaemia-induced hypertension and cardiac hypertrophy. Male rats received insulin glargine (InG) to induce hypoglycaemia followed by D-carnitine or acetyl-L-carnitine for carnitine depletion or carnitine supplementation, respectively. The obtained results showed that carnitine deficiency provoked hypoglycaemia-induced hypertension. Mean arterial pressure was elevated from 78.16 ± 11.4 to 100 ± 5.11 mm Hg in InG treated group, and from 78.2 ± 8.5 to 123.4 ± 28.2 mm Hg in InG + D-carnitine treated group. Acetyl-L-carnitine resisted the elevation in blood pressure in all hypoglycaemic animals and kept it within the normal values (68.33 ± 6.7 mm Hg). Acetyl-L-carnitine increased myocardial carnitine content leading to the attenuation of hypoglycaemia-induced oxidative stress, which was evaluated through measurement of the oxidative stress biomarkers such as inducible nitric oxide synthase, NAD(P)H quinone dehydrogenase-1, heme oxygenase-I, and glutathione S-transferase. Moreover, acetyl-L-carnitine prevented induction of gene expression of cardiac hypertrophy markers during hypoglycaemic conditions, which was assessed via the evaluation of mRNA expression of α-myosin heavy chain and β-myosin heavy chain. These findings demonstrate that carnitine might play an essential role in prevention of hypoglycaemia-induced hypertension and cardiac hypertrophy through providing energy and antioxidants to the cardiovascular system.

Insulin enhances renal glucose excretion: relation to insulin sensitivity and sodium-glucose cotransport

INTRODUCTION

Insulin regulates renal glucose production and utilization; both these fluxes are increased in type 2 diabetes (T2D). Whether insulin also controls urinary glucose excretion is not known.

METHODS

We applied the pancreatic clamp technique in 12 healthy subjects and 13 T2D subjects. Each participant received a somatostatin infusion and a variable glucose infusion to achieve (within 1 hour) and maintain glycemia at 22 mmol/L for 3 hours; next, a constant insulin infusion (240 pmol/min/kg) was added for another 3 hours. Urine was collected separately in each period for glucose and creatinine determination.

RESULTS

During saline, glucose excretion was lower in T2D than controls in absolute terms (0.49 (0.32) vs 0.69 (0.18) mmol/min, median (IQR), p=0.01) and as a fraction of filtered glucose (16.2 (6.4) vs 19.9 (7.5)%, p<0.001). With insulin, whole-body glucose disposal rose more in controls than T2D (183 (48) vs 101 (48) µmol/kg_FFM/min, p<0.0003). Insulin stimulated absolute and fractional glucose excretion in controls (p<0.01) but not in T2D. Sodium excretion paralleled glucose excretion. In the pooled data, fractional glucose excretion was directly related to whole-body glucose disposal and to fractional sodium excretion (r=0.52 and 0.54, both p<0.01). In another group of healthy controls, empagliflozin was administered before starting the pancreatic clamp to block sodium-glucose cotransporter 2 (SGLT2). Under these conditions, insulin still enhanced both glucose and sodium excretion.

CONCLUSIONS

Acute exogenous insulin infusion jointly stimulates renal glucose and sodium excretion, indicating that the effect may be mediated by SGLTs. This action is resistant in patients with diabetes, accounting for their increased retention of glucose and sodium, and is not abolished by partial SGLT2 inhibition by empagliflozin.

Effect of Insulin on Proximal Tubules Handling of Glucose: A Systematic Review

Renal proximal tubules reabsorb glucose from the glomerular filtrate and release it back into the circulation. Modulation of glomerular filtration and renal glucose disposal are some of the insulin actions, but little is known about a possible insulin effect on tubular glucose reabsorption. This review is aimed at synthesizing the current knowledge about insulin action on glucose handling by proximal tubules. Method. A systematic article selection from Medline (PubMed) and Embase between 2008 and 2019. 180 selected articles were clustered into topics (renal insulin handling, proximal tubule glucose transport, renal gluconeogenesis, and renal insulin resistance). Summary of Results. Insulin upregulates its renal uptake and degradation, and there is probably a renal site-specific insulin action and resistance; studies in diabetic animal models suggest that insulin increases renal SGLT2 protein content; in vivo human studies on glucose transport are few, and results of glucose transporter protein and mRNA contents are conflicting in human kidney biopsies; maximum renal glucose reabsorptive capacity is higher in diabetic patients than in healthy subjects; glucose stimulates SGLT1, SGLT2, and GLUT2 in renal cell cultures while insulin raises SGLT2 protein availability and activity and seems to directly inhibit the SGLT1 activity despite it activating this transporter indirectly. Besides, insulin regulates SGLT2 inhibitor bioavailability, inhibits renal gluconeogenesis, and interferes with Na+K+ATPase activity impacting on glucose transport. Conclusion. Available data points to an important insulin participation in renal glucose handling, including tubular glucose transport, but human studies with reproducible and comparable method are still needed.

Body fat change and 8-year incidence of hypertension: Korean Genome and Epidemiology Study

Hypertension is strongly correlated with an increased risk of cardiovascular events. Recent studies have demonstrated that body fat percentage (BF%) is associated with cardiometabolic risk factors. The aim of this study was to investigate the association between a change in BF% and body mass index (BMI) and the incidence of new-onset hypertension in a normotensive Korean cohort. At baseline (2001-2002), 8848 participants aged 40-70 years were recruited for the study; follow-up surveys were completed in the year 2012. A total of 3902 adults (1866 men and 2036 women) were included in the final analysis. These subjects were divided into quartile groups according to changes in BF% and were followed for 8.4 years to monitor for the development of hypertension. A Poisson regression model was used to evaluate the relative risk (RR) for hypertension according to BF% change quartile. Additionally, we also stratified participants into four groups according to BMI change levels and body fat change levels. Finally, we compared two factors, BF% change, and BMI change, to determine which is more predictive of incident hypertension. In an adjusted model, compared with the lowest BF% quartile group, the risk of new-onset hypertension significantly increased with BF% change: Changes in risk were 0%-2.0% for quartile 3 subjects (RR: 1.32 [1.06-1.63]) and 2.0%-8.9% for quartile 4 participants (RR: 1.78 [1.43-2.19]). We also revealed that the RR for new-onset hypertension was 1.81 (95% CI: 1.47-2.21) for quartile 4 group subjects, compared with subjects in quartile 1 (change in BMI -6.80 to -0.86% [kg/m2 ]). Body fat gain and BMI increase were predictors of hypertension in this community-based Korean cohort.

Angiotensin II-induced superoxide and decreased glutathione in proximal tubules: effect of dietary fructose

Angiotensin II exacerbates oxidative stress in part by increasing superoxide (O2-) production by many renal tissues. However, whether it does so in proximal tubules and the source of O2- in this segment are unknown. Dietary fructose enhances the stimulatory effect of angiotensin II on proximal tubule Na⁺ reabsorption, but whether this is true for oxidative stress is unknown. We hypothesized that angiotensin II causes proximal nephron oxidative stress in part by stimulating NADPH oxidase (NOX)4-dependent O2- production and decreasing the amount of the antioxidant glutathione, and this is exacerbated by dietary fructose. We measured basal and angiotensin II-stimulated O2- production with and without inhibitors, NOX1 and NOX4 expression, and total and reduced glutathione (GSH) in proximal tubules from rats drinking either tap water (control) or 20% fructose. Angiotensin II (10 nM) increased O2- production by 113 ± 42 relative light units·mg protein^-1·s^-1 in controls and 401 ± 74 relative light units·mg protein^-1·s^-1 with 20% fructose (n = 11 for each group, P < 0.05 vs. control). Apocynin and the Nox1/4 inhibitor GKT136901 prevented angiotensin II-induced increases in both groups. NOX4 expression was not different between groups. NOX1 expression was undetectable. Angiotensin II decreased GSH by 1.8 ± 0.8 nmol/mg protein in controls and by 4.2 ± 0.9 nmol/mg protein with 20% fructose (n = 18 for each group, P < 0.047 vs. control). We conclude that 1) angiotensin II causes oxidative stress in proximal tubules by increasing O2- production by NOX4 and decreasing GSH and 2) dietary fructose enhances the ability of angiotensin II to stimulate O2- and diminish GSH, thereby exacerbating oxidative stress in this segment.

PPARδ: A Potential Therapeutic Target for the Treatment of Metabolic Hypertension

High blood pressure and its associated cardiovascular diseases have been major risks for public health. Multiple metabolic risk factors can cause the vascular dysfunction and vascular lesion, and the hypertension due to metabolic disturbances was defined as metabolic hypertension. The members of a subfamily of the nuclear receptors, peroxisome proliferator-activated receptors (PPARs), were found to be key regulators of metabolism and vascular function. We provide up-to-date knowledge on the role of subtype PPARδ in the regulation of metabolism and vascular function and the effect of its intervention on the metabolic hypertension management. We hope to give some insights into the development of more effective treatments of metabolic hypertension and its main complications.

Telemedicine screening adolescent metabolic syndrome in Greek schools

BACKGROUND

Using telemedicine in the school setting in Greece, we screened a representative adolescent sample for MetS (International Diabetes Federation criteria) and explored its associations with anthropometric, sociodemographic and behavioural parameters.

MATERIALS AND METHODS

Cross-sectional data were obtained from 12- to 17-year-old high school students.

RESULTS

The prevalence of MetS in 1578 adolescents (mean age ± SD 14.4 ± 1.7 years) was 2.6% (3.4% among males; 2.0% among females), highest (4.3%) at age 13 years and lowest (1.3%) at 16 years. Adolescents with MetS had significantly higher mean body mass index (BMI) ± SD than those without MetS (30.2 ± 4.2 vs 21.3 ± 3.2 kg/m² , respectively; P < 0.001); among participants with obesity, 31.6% had MetS. Abdominal obesity, elevated triglycerides, low HDL-cholesterol, impaired fasting blood glucose (FBG) and elevated blood pressure (BP) were detected in 9.5%, 2.3%, 10.7%, 25.9% and 21.8% of participants, respectively. Additional analysis (modified NCEP:ATPIII youth criteria) demonstrated similar overall prevalence of MetS (2.9%). Statistically significant correlations were found between most anthropometric and MetS characteristics, with the exception of FBG, which was correlated only with systolic BP. BMI was strongly correlated with waist and hip circumferences (r = 0.818, P < 0.001; r = 0.825, P < 0.001, respectively). Single parenthood and older maternal age (>60 years) were risk factors for MetS. Although counterintuitive, body image distortion, body dissatisfaction and bullying about weight were more prevalent in normal weight girls.

CONCLUSIONS

The overall prevalence of MetS was low but 12-fold higher when obesity was taken into account. Impaired FBG and elevated BP were the most prevailing features. Telemedicine services were used effectively in Greek schools for screening youth MetS.